Wire supply device on a machine for spark erosion of workpieces

ABSTRACT

An electrode wire (20) is withdrawn from a pay-off spool (22), passed around guide rolls (24-30) to a machining span (32), and finally wound up on a take-up spool (40). The electrode wire (20) is guided in such a way that it always moves in the same plane at right angles to the axes, both when being wound up on the take-up spool (40) and when being unwound from the pay-off spool (22). Both spools (22, 40) are supported on a common carrier member (50) which is displaceable in axial direction of the spools (22, 40). A measuring device (70) is disposed between the pay-off spool (22) and the first guide roll (24) to detect deviations of the position of the electrode wire (20) from a predetermined position. The carrier member (50) is connected to a slide drive (60) which corrects any deviation detected of the position of the electrode wire (20) being unwound from the pay-off spool (22) by axially shifting the carrier member (50). Thus it also makes sure that the spent electrode wire (20) is wound up properly on the take-up spool (40).

The instant invention relates to a wire supply device on a machine forspark erosion of workpieces, comprising an electrode wire which iswithdrawn from a pay-off spool and passed around guide rolls to amachining span, the pay-off spool being rotatably supported on a pivotpin, the pivot pin being fastened to a carrier member which isdisplaceable in axial direction of the pay-off spool, a measuring meansbeing provided between the pay-off spool and the first guide roll todetect deviations of the position of the electrode wire from apredetermined position, and the carrier member being connected to aslide drive means which corrects any deviation detected of the positionof the electrode wire being unwound from the pay-off spool by axiallyshifting the carrier member.

BACKGROUND OF THE INVENTION

In the case of a known wire supply device of this kind (DE 89 12 810 U1)the axial slidability of the pay-off spool containing a wire supply isbased on the finding that oscillations may be induced at the guide rollwhich immediately follows the pay-off spool, and these oscillations maybe transmitted to the machining span where they may affect the accuracyto size and the surface quality of the workpieces being processed. Whenthe pay-off spool is supported so as not to be movable axially, suchoscillations are caused by the fact that the electrode wire, arranged inlayers on the spool, is payed off at a different angle at the beginningof each layer than at the end of the layer. From a certain angle on, theelectrode wire tends to move up periodically on flanks of a grooveformed in the guide roll which receives the wire next down the line fromthe pay-off spool and then to slide down again into the bottom of thegroove. With the known device of the generic kind in question this isprevented by controlled shifting of the pay-off spool so that theelectrode wire constantly maintains a certain position at which it runsperpendicularly to the axis of the pay-off spool.

It is also known (JP 07 001 247 A) to wind up spent electrode wire on atake-up spool for disposal, causing the spool to carry out controlledaxial reciprocating movements during the winding process in order tomake full use of the winding space available.

SUMMARY OF THE INVENTION

The invention starts from the finding that oscillations may be generatedalso during the winding up of the used electrode wire and that theseoscillations may propagate as far as the machining span where they mayaffect the accuracy to size and surface quality of the workpiece beingprocessed.

It is the object of the invention to prevent such oscillations as well.

This object is met, in accordance with the invention, in a wire supplydevice of the kind specified initially by the fact that

a take-up spool for winding up the used electrode wire is supported on asecond pivot pin,

the second pivot pin is fastened to the carrier member in parallel withthe first pivot pin,

both spools are axially fixed with respect to their own pivot pins, and

the electrode wire is guided in such manner that it always moves in thesame plane normal to the axes when being wound up on the take-up spooland also when being unwound from the pay-off spool.

As a result, the electrode wire is wound up on the take-up spool in thesame layered fashion as it was wound originally on the pay-off spool.The original wound configuration of the electrode wire on the pay-offspool thus is reproduced on the take-up spool by the mere fact that themeasuring means which monitors only the unwinding electrode wire effectscontrol of the common carrier member of both spools. In this manner theelectrode wire is prevented from slipping off a previously laid wirewinding on the take-up spool and thereby starting to oscillate.

The device according to the invention preferably is developed further byproviding that

the measuring means comprises a measuring roll which is supported inparallel with the axis of the pay-off spool for free axial movement andhas an annular groove to guide the electrode wire, and that

the measuring means further comprises sensors which emit signals forcorrection to the slide drive means when the measuring roll deviatesfrom a normal axial position.

The sensors preferably are inductive proximity switches.

It is of advantage if the slide drive means comprises a servo motor anda spindle drive.

Finally, it is convenient if the two spools are connected to a motoreach, mounted on the carrier member, and acting so as to drive thetake-up spool and retard the pay-off spool, both motors being controlledso that the electrode wire is kept under essentially constant tension.

BRIEF DESCRIPTION OF THE DRAWING FIGURES

The invention will be described further, by way of an example withreference to the accompanying drawings, in which:

FIG. 1 is a side elevation of a spark erosion machine comprising adevice according to the invention;

FIG. 2 is an enlarged cutout of FIG. 1;

FIG. 3 is a vertical section along line III--III of FIG. 2;

FIG. 4 is a horizontal section along line IV--IV of FIG. 2.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

The device illustrated in the drawing comprises a casing 10 which ismovable under numerical control along a horizontal axis Y, such as iscustomary with erosive machinery (e.g. DE 41 15 107 C2). The casing 10is formed with a guide means 12 to guide a carriage 14 which is movableunder numerical control along a vertical axis W. The carriage 14 carriesa tool head 16 which is rotable about a vertical axis E, while beingcontrolled numerically too. A fork-shaped wire holder 18 for anelectrode wire 20 is fastened to the tool head 16.

Below the tool head 16, a tool support is arranged for vertical slidingmovement and rotational movement about a horizontal axis in a mannerknown from DE 41 15 107 C2, for example, and therefore not shown in thedrawing.

The electrode wire 20 is supplied from a pay-off spool 22 on which it iswound in conventional manner in closely adjacent windings layered on topof each other. Guide rolls 24 and 26 are supported at the casing inparallel with the pay-off spool 22. The electrode wire 20 first passesaround the guide rolls 24 and 26, then around guide rolls 28 and 30which are supported at the carriage 14, and next, while being guided byfurther guide rolls, the electrode wire 20 travels substantiallyvertically downwards to the wire holder 18 where it passes through amachining span 32 in the center of which it crosses the axis of rotationE. From the machining span 32, the electrode wire 20 moves aroundanother guide roll 34 supported at the carriage 14 and finally aroundguide rolls 36 and 38 which are supported at the casing 10 with theiraxes parallel to the axes of the guide rolls 24 and 26, travelling on toa take-up spool 40 which is supported below and paraxial with thepay-off spool 22.

The pay-off spool 22 and the take-up spool 40 each are supported on apivot pin 42 and 44, respectively. However, in operation a respectivelocking screw 46 or 48 prevents them from becoming axially displacedwith respect to the corresponding pivot pin. The locking screws 46 and48 are loosened only for exchanging the pay-off spool 22 and the take-upspool 40, respectively. The two pivot pins 42 and 44 are fastenedhorizontally and parallel to each other at a carrier member 50 in such away that the winding spaces of the two spools 22 and 40 are locateddirectly above each other. The carrier member 50 is embodied by avertical plate and is guided by a guide bushing 52 fixed to it on ahorizontal guide rod 54 which is secured to the casing 10. Rotation ofthe carrier member 50 about the guide rod 54 is prevented by two guiderolls 56, each rotatably supported on a corresponding vertical axis onthe carrier member, at the greatest possible distance from the guide rod54. Parallel to the guide rod 54, a guide bar 58 is fixed to the casing10 between the two guide rolls 56.

A slide drive means 60 is coordinated with the carrier member 50 andcontrolled in such manner that the electrode wire 20 always is advancedto the guide rolls 24 and 26 at right angles to the axes of rotationthereof and is wound on the take-up spool 40 in the same closelyadjacent windings, super-positioned in layers, as it was withdrawn fromthe pay-off spool 22. The slide drive means 60 comprises a servo motor62 connected by a belt drive means 64 to a threaded spindle 66 which isdisposed in parallel with the axes of rotation of the pay-off andtake-up spools 22 and 40, respectively. Together with a threaded nut 68formed in the carrier member 50, the threaded spindle 66 presents athread drive means which is free from play. Consequently, the positionof the carrier member 50 and thus also the positions of the pay-offspool 22 and take-up spool 44 can be controlled with great precision bymeans of the servo motor 62.

The slide drive means 60 forms part of a control circuit which alsoincludes a measuring means 70 with a measuring roll 72. The measuringroll 72 is supported on a pivot pin 74 parallel to the pivot pins 42 and44 so as to be freely rotatable and freely movable in axial direction.Any axial shifting of the measuring roll 72 on the pivot pin 74 ismonitored by sensors 76 and 78 which are secured to the casing 10.

Rotation of the spools 22 and 40 is controlled by a rotary drive controlmeans 80 in such a manner that the electrode wire 20 is kept undersubstantially constant tension at all times. The control means 80controls both a motor 82 which normally acts via a belt drivearrangement 84 on the pay-off spool 22 so as to retard it, and a motor86 which normally acts via a belt drive arrangement 88 on the take-upspool 40 so as to propel the latter. As both motors 82 and 86 aresecured to the carrier member 50,they take part in the movements of thelatter in the direction of the axes of both spools 22 and 40.

Before reaching the guide rolls 24 and 26, the electrode wire 20 comingfrom the pay-off spool 22 travels through an annular groove of V-shapedcross section formed in the measuring roll 72. Therefore, the positionof the measuring roll on the pivot pin 74 is variable by axial forceexerted by the electrode wire 20 on the measuring roll 72. This axialforce is of zero magnitude only when the electrode wire 20 is travellingin a plane which is perpendicular to the axes of rotation of the pay-offspool 22 and the two guide rolls 24 and 26, i.e. vertical in the exampleshown. Any deviation from this desired condition will cause axialdisplacement of the measuring roll 72 on its pivot pin 74 and, as aresult thereof, one or the other sensor 76 or 78, depending on thedirection of the axial shifting, will emit a signal to the servo motor62 causing it to rotate in one or the other direction in order toreestablish the desired condition. It may be taken from FIGS. 3 and 4that the carrier member 50 is shifted back and forth along the guide rod54 as the individual wire layers formed by the electrode wire 20 woundon the pay-off spool 22 are being used up. The distance by which thecarrier member 50 including the pay-off spool 22 and the take-up spool40 is being reciprocated is commensurate with the width of the windingspace of these spools.

As a result of the joint displacement of the two spools 22 and 40, theelectrode wire 20 being wound up on the take-up spool 40 always moves inthe same plane E, which is vertical in the embodiment illustrated here,as it leaves the pay-off spool 22. In this manner any tendency isprevented that the electrode wire 20 might climb up on the laterallimitations of the groove guiding it around the guide roll 24 or thesuccessive guide rolls. On the other hand, the electrode wire 20 iswound on the take-up spool 40 in windings which are just as closelyplaced next to and on top of each other as they were on the pay-offspool 22. The orderly arrangement of the electrode wire as usuallyoriginating from the wire manufacturer thus is copied, so to speak, onthe take-up spool 40. For this reason, the electrode wire has no chance,either on the take-up spool 40 or on the pay-off spool 22, to slip off awire winding or get caught between two wire windings, thereby inducingoscillations.

We claim:
 1. A wire supply device on a machine for spark erosion ofworkpieces, comprisingan electrode wire (20) which is withdrawn from apay-off spool (22) and passed around guide rolls (24-30) to a machiningspan (32), the pay-off spool (22) being rotatably supported on a pivotpin (42), the pivot pin (42) being fastened to a carrier member (50)which is displaceable in axial direction of the pay-off spool (22), ameasuring means (70) to detect deviations of the position of theelectrode wire (20) from a predetermined position being provided betweenthe pay-off spool (22) and the first guide roll (24), the carrier member(50) being connected to a slide drive means (60) to correct anydeviation detected of the position of the electrode wire (20) beingunwound from the pay-off spool (22) by axially shifting the carriermember (50), a take-up spool (40) for winding up the electrode wire (20)supported on a second pivot pin (44), the second pivot pin (44) fastenedto the carrier member (50) in parallel with the first pivot pin, andboth spools (22, 40) are axially fixed with respect to their own pivotpins (42, 44), whereby the electrode wire (20) is guided in such mannerthat it always moves in the same plane normal to the axes when beingwound up on the take-up spool (40) and also when being unwound from thepay-off spool (22).
 2. The device as claimed in claim 1, wherein themeasuring means (70) comprises a measuring roll (72) which is supportedfor free axial movement and in parallel with the axis of the pay-offspool (22) and has an annular groove to guide the electrode wire (20),andthe measuring means (70) further comprises sensors (76,78) which emitsignals for correction to the slide drive means (60) when the measuringroll (72) deviates from a normal axial position.
 3. The device asclaimed in claim 2, characterized in that the two spools (22, 40) areconnected to a motor (82, 86) each, arranged on the carrier member (50)and acting so as to drive the take-up spool (40) but to retard thepay-off spool (22), both motors (82, 86) being controlled so that theelectrode wire (20) is kept under essentially constant tension.
 4. Thedevice as claimed in claim 2, characterized in that the slide drivemeans (60) comprises a servomotor (62) and a threaded spindle (66). 5.The device as claimed in claim 4, characterized in that the two spools(22, 40) are connected to a motor (82, 86) each, arranged on the carriermember (50) and acting so as to drive the take-up spool (40) but toretard the pay-off spool (22), both motors (82, 86) being controlled sothat the electrode wire (20) is kept under essentially constant tension.6. The device as claimed in claim 2, wherein the sensors (76, 78) areinductive proximity switches.
 7. The device as claimed in claim 6,characterized in that the slide drive means (60) comprises a servomotor(62) and a threaded spindle (66).
 8. The device as claimed in claim 7,characterized in that the two spools (22, 40) are connected to a motor(82, 86) each, arranged on the carrier member (50) and acting so as todrive the take-up spool (40) but to retard the pay-off spool (22), bothmotors (82, 86) being controlled so that the electrode wire (20) is keptunder essentially constant tension.
 9. The device as claimed in claim 6,characterized in that the two spools (22, 40) are connected to a motor(82, 86) each, arranged on the carrier member (50) and acting so as todrive the take-up spool (40) but to retard the pay-off spool (22), bothmotors (82, 86) being controlled so that the electrode wire (20) is keptunder essentially constant tension.
 10. The device as claimed in claim1, characterized in that the slide drive means (60) comprises aservomotor (62) and a threaded spindle (66).
 11. The device as claimedin claim 10, characterized in that the two spools (22, 40) are connectedto a motor (82, 86) each, arranged on the carrier member (50) and actingso as to drive the take-up spool (40) but to retard the pay-off spool(22), both motors (82, 86) being controlled so that the electrode wire(20) is kept under essentially constant tension.
 12. The device asclaimed in claim 1, characterized in that the two spools (22, 40) areconnected to a motor (82, 86) each, arranged on the carrier member (50)and acting so as to drive the take-up spool (40) but to retard thepay-off spool (22), both motors (82, 86) being controlled so that theelectrode wire (20) is kept under essentially constant tension.